1. Field of the Invention
The present invention relates to an underwater pelletizer and more specifically to a cutter hub and blade assembly supported and driven for rotational movement and axial movement in relation to the die face of a die plate in an underwater pelletizer. The supporting and driving arrangement for the cutter hub and blades includes a positive control of axial movement of the cutter hub and blades in relation to the die face as the cutter hub and blades are moved toward and away from the die face to obtain and maintain axial adjusted positions of the cutter hub and blades to minimize wear on the mechanical components involved. Positive control of the axial movement of the cutter hub and blades is obtained by a hydraulic/pneumatic actuation system controlling a motion rod extending through a driven hollow motor shaft with one end of the motion rod connected with a hydraulic/pneumatic control and the other end being rigidly connected to a cutter hub holder that supports the cutter hub and blades to move the cutter hub and blades toward and away from the die face.
2. Description of the Prior Art
Underwater pelletizers including a cutter hub holder supporting a cutter hub and blades associated with a die face in order to rotate the blades to cut strands of extruded polymer into pellets within a water box through which water is circulated to cool and harden the pellets and convey a slurry of pellets to an outlet in the water box are well known. Prior U.S. Pat. No. 6,332,765 issued Dec. 25, 2001 for Cutter Hub Holder discloses a cutter hub holder, cutter hub and blades biased toward the die plate by variable pressure through a resilient structure incorporated into supporting and driving engagement with the cutter hub and blades. The present invention comprises an improvement over the cutter hub holder disclosed in aforesaid U.S. Pat. No. 6,332,765 which, together with the prior art of record therein are incorporated herein by reference as if fully set forth herein.
In U.S. Pat. No. 6,332,765, the cutter hub holder is connected to and supports the cutter hub and blades and is drivingly connected to a motor shaft. The motor shaft extends through an electric motor and is hollow throughout its length. One end of the motor shaft is communicated with a stationary rotary transmission lead that is communicated with a source of fluid pressure through a pressure regulating valve. The hollow motor shaft includes a piston and piston rod moveable in the interior of the hollow motor shaft which defines a cylinder for the piston to move the piston and piston rod axially in relation to the motor shaft. The piston rod is connected to a cutter hub holder through a resilient device, such as a spring, to bias the cutter hub holder, cutter hub and blades thereon toward the die face. This structure provides an axial force to move the cutter hub and blades toward the die plate but does not provide any force to move the cutter hub and blades axially away from the die face. Further the prior art does not provide a mechanism for positively controlling the movement of the cutter hub and blades toward and away from the die plate.